White powder on vent

[J. Brent Heberlein]

While inspecting a gas forced-air furnace, I observed a white powder looking material gowing out from the joints on the flue vent. The material looked like a crystal growing, very delicate. Can someone tell me what causes this to grow, what it is, and is it toxic? I have talked with our local gas utility company and they are not much help!

[wforsyth]

Doug fixed it.

[Doug Edwards]

http://www.nachi.org/forum/archive/i...hp/t-3150.html

[Kevin Mikottis]

I just found this yesterday. This seems more like what was originally described. It seems like what was described as a combustion / flue venting issue in the other thread.
Can someone confirm that would be the cause in my image.